186 Observations regarding Fossil Infusoria. 



(Gaillonella distans). The Podosphenia nana, n. sp., Navicida 

 scalprum ? and Bacillarm mdgaris (the two last are recent ma- 

 rine species) occur singly between the individuals of the pre- 

 vailing species, and the first only can sometimes be compared 

 to the Gaillonella for abundance. In the same polishing slate 

 there occur impressions of plants and one species of fish, the 

 Leuciscus papyraceus of Bronn, according to Agassiz. In the 

 adhesive slate of Menilmontant, some indistinct traces were 

 found of the Gaillonella distans. An individual of this animal, 

 which, almost without any uniting basis, constitutes the polish- 

 ing slate of Bilin, is 2 1 of a line in size ; many are smaller ; there 

 are consequently forty-one thousand millions of these animals in 

 one cubic inch of that substance. 



SCIENTIFIC INTELLIGENCE. 



METEOROLOGY. 



1. Upon a new Thermometer which will indicate Mean 

 Temperatures. In a Letter from M. Jules Jiirgensen to M. 

 Arago. Our common thermometers indicate the temperature 

 at the time that we make our observation ; and there are others 

 which supply the maximum and minimum temperatures from 

 the time we have made one observation till the time when we 

 again examine them. Up to the present day, no thermometer 

 has been constructed which would indicate with precision the 

 mean temperature of a day, or month, or year. This, how- 

 ever, is the design which M. Jules Jiirgensen, a celebrated 

 watchmaker at Copenhagen, undertook to accomplish, and which 

 he has succeeded in fulfilling. The balance-wheel of a common 

 watch increases in size when the temperature increases, and, on 

 the contrary, contracts when the temperature diminishes. An 

 augmentation in the dimensions of the balance-wheel leads in- 

 evitably to an increase of the duration of its oscillations, and 

 consequently to the watch going slower, whilst its contraction 

 makes it go quicker. To meet these inconveniences, watch- 

 makers have long been in the habit of substituting for simple 

 balance-wheels, which are formed of four radii and a conti- 

 nuous ring all of one metal, others which are compound. 



